In this paper, a 3-D realistic numerical breast model is developed from MRI images of a typical Asian woman's breast. The breast outline is identified by edge detection algorithm and the breast interior is segmented into several tissue types based on the gray value of the pixels. The electrical properties of normal breast tissues are chosen according to the measurement results. The derived model is compatible with FDTD algorithm and the simulation of the breast cancer detection is conducted. Imaging results demonstrate the feasibility of the breast model and the imaging algorithm.